Chip quartz oscillator and liquid-phase sensor

ABSTRACT

The present invention relates to a chip quartz oscillator. In an embodiment of a chip quartz oscillator S in accordance with the present invention, a quartz oscillator  2,  which has a detection electrode  3  on a surface thereof and a non-detection electrode on the other surface thereof, is fixed on a substrate  1,  and each of the electrodes is connected electrically to a terminal  4  or  4 ′ on the substrate  1.  While keeping the non-detection electrode in contact with the substrate  1,  the quartz oscillator  2  is fixed on the substrate  1,  by flexibly bonding the side-wall  2 ′″ of the quartz oscillator  2  along its circumference to the surface of the substrate  1  by using the elastic bonding agent  5.  Thus, the oscillation surface of the quartz oscillator  2  is supported distributively on the substrate  1  in a surface-contacting and non-adhesive manner.

TECHNICAL FIELD OF INDUSTRIAL APPLICATION

The present invention relates to a quartz oscillator sensor and anoscillation circuit for a liquid-phase sensor in which an elastic waveelement such as quartz oscillator is used as a detector immersed in aliquid medium.

PRIOR ART

Piezoelectric acoustic wave devices such as quartz oscillator can beutilised as mass sensors on the basis of the principle that a materialadsorbed on the electrode surface changes the fundamental oscillationfrequency of the oscillator in proportion to the mass of the adsorbate;the change has been proven experimentally to conform to the theoreticalformula proposed by Sauerbrey (Sauerbrey, G., Z. phys. 155 (1959), p.206-222). Owing to the high detection sensitivity predicted by theformula, a micro-measurement method using such a sensor is far superiorto general mass measurement methods using mechanical balances, and thusthe method has been put into practical use, for example, in quantitativemeasurement of odorous molecules or aerosols in the gaseous phase.

A quartz oscillator is generally a circular or rectangular crystallineplate shaped by cutting along a particular crystal face for a naturalcharacteristic oscillation of the crystal and is provided withelectrodes made of thin layers of vapour-deposited metal. Depending uponits cutting angle, each crystal plate is designated as an AT, BT, CT, X,or Y cut. The quartz plate is situated between a pair of thin-layermetal electrodes placed symmetrically in parallel. An inductionelectrical field between the electrodes results in distortion in thequartz crystal, whereas a distortion produces an electrical charge; theso-called piezo-electrical phenomenon achieves the reversible and steadyoscillation.

Usually, the surface area of the quartz plate is wider than that of theelectrode. The non-electrode area without the piezo-electrical effect onthe quartz plate helps to propagate the elastic wave occurred at theelectrode area while moderately attenuating the wave. Thus, it is anarea that is responsible for the so-called “confinement effect.” Thus,in designing quartz oscillators, the selection of shape and size of thequartz plate is most important in order to reduce unfavourablesub-oscillations such as spurious oscillations caused by adverse effectssuch as end-face reflection of the plate, etc.

A means of mechanical fixation is necessary for mounting such a quartzoscillator for use as a sensor. A quartz oscillator element for use asan electronic component used in the gaseous phase is usually designed tobe supported by a minute contact area of the quartz plate end face byusing a supporting metal lead in order to lower the stress as far aspossible in both the directions of the radius and the thickness of thequartz plate. In other words, the elastic wave is attenuated in thevicinity of the end face and the influence of the mounting forces issmall; the contact area is taken into consideration to reduce the areaas much as possible so as not to impose the mounting forces on thequartz plate.

The first liquid-phase elastic wave element sensor was reported byBasstiaans and his colleague in 1980 (Konash, P. L. and Bastiaans, G.J., Anal. Chem. 52 (1980), p. 1929-1931). Ever since the first report,many studies have been reported on elastic wave element sensorsoperating in the liquid phase; the technology is expected to beapplicable to detect substances, as targets under test, includingpharmaceutical agents usually dissolved in the liquid phase, andchemical substances such as agricultural pesticides and food additives,as well as bio-functional molecules represented by nucleic acids such asDNA and RNA, and proteins such as antibodies, hormone receptors, andlectins, which function only in the liquid phase.

However, a problem occurs when the quartz oscillator, which is anelectrical element originally designed on the assumption of using it ina gaseous phase, is used as a sensor in a conducting solution—namely anelectrical short-circuit occurs between the electrodes in solution. Inall the previous studies, without exception, it has been necessary totake measures to prevent this short-circuit. Specifically, in aliquid-phase quartz oscillator sensor, the one of the pair of electrodeswhich acts as a detection surface is exposed to the liquid phase, whilethe other electrode is protected in some way against coming into contactwith the solution. Of course as the quartz oscillator is an elementwhich is based on the principle of a constant stable elasticoscillation, any mechanical constructions to prevent the electrode fromcoming into contact with the solution, which interfere with theoscillation of the quartz oscillator, should be definitely avoided.

The high-quality frequency stability of a quartz oscillator as anelastic wave element is represented by a high Q (quality factor). The Qmarkedly decreases as the degree of interference with the oscillation ofthe quartz oscillator increases. In addition, in the liquid-phasesensor, in which the quartz plate is exposed to a liquid with a highviscosity as compared with gas, being in contact with liquid itself mayhave an interfering effect and, as a consequence, the Q may decreasegreatly; the Q may also decrease to the minimum due to an impropermechanical construction. In other words, in the worst case theoscillation might stop.

For example, there is a method, as frequently found in study reports onthe development of devices with quartz oscillators (for example, Masson.M. et al., Anal. Chem. 67 (1995), p. 2212-2215, U.S. Pat. No. 5,135,852,etc.), by which one of a pair of electrodes alone is allowed to come incontact with liquid; a circular quartz oscillator is fixed with a pairof rubber O-rings or gaskets placed on both sides thereof. FIGS. 14 and15 show the positional relationship between the quartz plate and theO-ring in a quartz oscillator sensor in typical prior art example. FIG.14 is a plan view from above, and FIG. 15 is a sectional view along lineG-H in FIG. 14. In these figures, the quartz oscillator 48, which iscircular in shape and has a pair of electrodes in both sides thereof, isplaced between a pair of O-rings or gaskets 49, and installed in theflow-type liquid-phase quartz oscillator sensor 50 as indicated in FIG.16. FIG. 16 contains an inflow entrance 51, a drain hole 52, and acircuit board 53.

In FIGS. 14-16, the O-rings or gaskets 49 act to prevent the solutionflowing into the cavity where the non-detecting electrode is present, aswell as to fix the quartz oscillator to the inside wall of themeasurement cell containing the solution. In this method employed in theprevious example, a mounting point is chosen on a surface of the quartzplate in the vicinity of its end face where the oscillation is hardlyinterfered with and the quartz plate is fixed via the elastic rubber,resulting in secure protection against leaks and a flexible mounting.However, the adjustment of the tightening pressure for the O-ring orgasket 49 is so delicate that reproducibility is unable to be expected.Furthermore, the quartz plate itself is handled directly when it isbeing placed between the O-rings or gaskets 49 in a narrow flowcell, andtherefore, there is a risk of damaging the fragile quartz plate. Evenwhen fixed firmly, the quartz oscillator might be distorted due topressure fluctuations in the solution being tested. These act on thequartz plate, and because there is usually a cavity on the side ofnon-detection electrode of the quartz plate, deflect the middle of thequartz plate towards and away from the cavity. Moreover, in the case ofthe infinitesimal deformations of the vessel caused by temperaturechanges or hydraulic pressure changes, the quartz plate is directlystressed by such deformations. In any event, such deformations of thequartz oscillator resulted in a marked decrease in the Q and an unsteadyoscillation in the liquid-phase sensor; many examples have shown thatthe oscillation halts in the worst case.

For example, Japanese Patents No. 2759659, No. 2759683 and No. 2759684disclose applications in a liquid-phase sensor of a quartz oscillatorwith a barrier on one side covered with elastic and plastic materials.In this example, the quartz plate is hardly subjected to the mountingforces in the structure, because the covering is fixed adhesively at thecontact positions similar to those of the above-mentioned O-ring and thequartz oscillator. However, a relatively large amount of sample solutionis required for the measurement, even when it is possible to immersesuch a bulky structure (i.e. the quartz oscillator with the covering) inthe sample solution. This, as a matter of course, limits the range ofobjects testable by the liquid-phase sensor; it is unsuitable formeasurements in which only a small amount of sample is available for thedetection of substances including the above-mentioned bio-functionalmolecules. Changing the sensor to a flow-type sensor effectivelyimproves the apparent desensitisation due to an apparent increase inamount of sample solution, thereby markedly reducing the actual amountof sample solution required. However, it is difficult to install thequartz oscillator with the components as disclosed in theabove-mentioned patent into a flow cell, and even if it were possible,further efforts are required to design the device in which a quartzoscillator itself is not subjected to deformation forces from thefixation vessel.

The theoretical sensitivity of the liquid-phase quartz oscillator sensoris defined uniquely according to the above-described Sauerbrey'sformula, where the fundamental oscillation frequency and the area of theelectrode are variables. However, the practical effective sensitivity ofa liquid-phase quartz oscillator sensor, although defined based on thetheoretical sensitivity, depends on the normal response to an increasein mass on the electrode of the quartz oscillator, or it depends on howthe minimal change of time changes (decrease) in signal frequency can bedetected as a significant change. In other words, the above-mentionedeffective sensitivity largely depends on the existence and the degree ofinfluence of insignificant signals such as noises and drifts, which masksmall time changes in signal frequency.

As described above, when a quartz oscillator is placed in a solution,the energy dissipation rate is elevated and effective impedanceincreases; the Q decreases greatly when compared with the quartzoscillator placed in a gas phase. This property is inevitable for theapplication. This means impairment of the frequency maintenance abilityor the high buffer action, which is an original property of the quartzoscillator, against the change of electrical load of applied voltage,etc. or against the change of mechanical load resulted from the changein the physical properties (pressure, viscosity, etc.) of solution incontact with the device. As compared with the quartz oscillator placedin a gas phase, a sensor operating in a liquid phase displays a lot ofnoise and/or large drifts, because its output signal changes easilyaccording to the load fluctuations as described above. Thus, when usualquartz oscillator circuits, which had been developed on the assumptionthat the oscillation occurs in a gas phase, were used in liquid-phasesensors without any modification, steady oscillation was oftenimpossible to achieve.

Moreover, since the liquid-phase quartz oscillator sensor is often usedas a chemical sensor or a biosensor, the sample solution is usually anelectrically conducting fluid that contains electrolytes; thus itsdetection electrode is always exposed to such an electrically conductingfluid. This has been recognised by persons who have developedliquid-phase quartz oscillator sensors, and several measures to solvethe problem have been proposed by them. In addition, sensors with highersensitivity and higher-throughput performance have been demanded owingto the recent advancement of technology of molecular biology andanalytical chemistry. Device multiplexing in a sensor has madesimultaneous multi-measurement commonplace. The device-multiplexingtrend requires measures against another type of short-circuit besidesthe above-mentioned problem of short circuit between a pair ofelectrodes in a single quartz oscillator in the oscillation circuitsystem that drives the sensor. Specifically, it is necessary to dealwith the problem of short-circuit caused by a common electrical groundshared by the oscillation circuits corresponding to the respectiveelectrodes when multiple electrodes are simultaneously immersed into aconducting solution.

For example, Unexamined Published Japanese Patent Application (JP-A) No.Hei 11-163633 has disclosed the example of obtaining the amplificationdegree required for the quartz oscillation in a liquid by connectingthree inverters in series to an amplifier circuit. This example is basedon designing energy compensation for the loss of energy dissipated intothe liquid phase by that gained by the amplification. Similarly designedcircuits have also been proposed in a report of Barnes and his colleague(Barnes, C., Sens. Actuators A., 29 (1991), p. 59-69) and U.S. Pat. No.4,788,466. These publicly known technologies can be assumed as aneffective strategy when the energy is dissipated markedly, and thus, thequartz oscillator halts, but the Q of quartz oscillator is not improvedbased on the strategy. Because of this, it is ineffective for noisesfrom the concomitant devices, for example, noise directly transmittedfrom the DC power source unit for rectification and voltage drop down ofthe power from the AC line or transmitted from output-signal processingsystems as well as fluctuations of applied power voltage due toradiation noise around the quartz oscillator. Thus, improvement of theeffective sensitivity cannot be achieved by these methods. In addition,device multiplexing, specifically, the arrangement of multipleoscillation circuits in a single device unit has not been assumed in theabove-mentioned disclosed technologies.

An example of circuit using a battery and photocoupler has been proposedin a report of Bruckenstein and his colleague (Bruckenstein, S. andShay, M., Electrochimica Acta, 30 (1985) p. 1295-1300). However, thisexample is not designed for device multiplexing, and the signals from apair of differentially operating quartz oscillator sensors, of which oneis for sample measurement and the other is for reference measurement,are connected directly inside the closed circuit. Thus, there is theproblem of short-circuits between the oscillation circuits that occur asthe pair of quartz oscillator sensors is immersed into the samesolution. Further, an example of circuit, using a battery as a powersource and having a transformer inserted in its signal system, has beenproposed in U.S. Pat. No. 3,561,253. In this example of circuit, theinsulation is achieved by using the transformer, and therefore, it has asmall effect on the noises from external signal processing system or theinfluences of load fluctuation, but it cannot remove the elements ofalternating noise such as high frequency noise, etc.

Problems to be Solved by the Invention

As described above, when an elastic wave element such as a quartzoscillator is used as a liquid-phase sensor, oscillation with a low Q(for example, a Q of 2000 or less as compared to Qs of up to 100000which can be achieved for quartz oscillators used in the gaseous-phase)should be expected because mechanical load increases by contact withliquid, which is inevitable for the application. To achieve highperformance, multi-functionality and high reliability of sensors whichare forced to operate under the condition of a low Q, it is necessary todesign the electrical and physical configuration by taking intoconsideration the following points: (1) further decreases in Q should beavoided by keeping the mechanical stress load on the oscillator, whichresults from the mounting of the oscillator in the cell, to a minimum;(2) unfavourable external load variations should not be passed to thequartz oscillator without autonomous buffering capacity (tolerance tothe load fluctuation) required for outputting the stable signalfrequency. In other words, in order to ensure a stable oscillationfrequency from the quartz oscillator, the voltage supplied to theoscillator must be constant as even a change of less than 1 mV in the DCvoltage of, for example 5V, applied to the oscillator results in asignificant loss of frequency stability. Therefore, the power supply tothe quartz oscillator should be arrange such that voltage is constant toan accuracy of 1 mV or better, no matter what happens in order toprevent input voltage-dependent, undesirable frequency changes; and (3)noise should not be transmitted in. In addition to these, in thisconfiguration, not only should insulation should be ensured between theelectrodes on a single quartz oscillator but also the requirement ofelectrical isolation of each oscillation system should be satisfied bypreventing short circuits between the electrodes through the solution,or short circuits between conducting materials in contact with a liquidand other devices through a common electrical ground or staticconnection when multiple quartz oscillators are present. It has been aproblem to meet these conditions in the prior art and the purpose of theinvention is to provide a quartz oscillator which overcomes some or allof these problems.

DISCLOSURE OF THE INVENTION

In the present application of the invention, a new design is presentedwhich attempts to overcome these problems that were unsolved by theprior art.

Thus an object of the present invention is to provide a chip quartzoscillator in which the quartz oscillator is prevented from beingdistorted by external deformation forces.

A further object of the present invention is to provide a combinedquartz oscillator element, in which multiple chip quartz oscillators canbe arranged on a common mounting substrate.

Another object of the invention is to provide chip quartz oscillators inwhich the provision of a flexible mounting is provided by means whichcan easily accommodate variations in size of the quartz oscillators.

A further object of the present invention is to provide chip quartzoscillators in which the quartz oscillator mounting forces are spreadevenly over the circumference of the quartz oscillator.

An additional object of the present invention is to provide chip quartzoscillators in which liquid is prevented from coming into contact withthe non-detection electrode of the quartz oscillator.

Another object of the present invention is to provide chip quartzoscillators in which the quartz oscillator is supported by a substratewithout the oscillation of the quartz oscillator being affected by thesubstrate.

An additional object of the present invention is to provide chip quartzoscillators in which the quartz oscillator oscillation is not degradedby the stiffness of the mounting mean.

Yet a further object of the present invention is to provide a batch-typeliquid-phase quartz oscillator sensor in which a steady oscillation isachieved and unaffected by the pressure fluctuation of the solution.

Another object of the present invention is to provide a flow-typeliquid-phase quartz oscillator sensor, in which an unfavourable pressureexerted by mounting is not applied to the fixed quartz oscillator and inwhich insulation is ensured between the electrodes of quartz oscillator;which sensor has a detection cell for liquid to be tested and works withonly the detection electrode on the quartz oscillator surface immersedin a flowing liquid; and in which steady oscillation is achieved andunaffected by the pressure fluctuation of the solution caused by flowrate fluctuation.

Yet another object of the present invention is to provide a quartzoscillator device, with means for preventing the fluctuation ofoscillation frequency resulted from the variation of power sourcevoltage caused by external noises and achieving a steady oscillation;and which helps to improve the effective sensitivity of a liquid-phasesensor.

A further object of the present invention is to provide a method formaking quartz oscillator devices in accordance with the presentinvention.

The present invention will be illustrated below by means of examples ofembodiments of the invention and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view from above schematically showing a firstembodiment of a chip quartz oscillator in accordance with the presentinvention.

FIG. 2 is a sectional view along the line A-B in FIG. 1.

FIG. 3 is an enlarged view of the circled part of FIG. 2.

FIG. 4 is a plan view from above schematically showing a secondembodiment of a chip quartz oscillator in accordance with the presentinvention.

FIG. 5 is a sectional view along the line C-D indicated in FIG. 4.

FIG. 6 is a sectional view of a flow-type liquid-phase quartz oscillatorsensor in which a chip quartz oscillator in accordance with the presentinvention is installed.

FIG. 7 is a plan view from above of a chip quartz oscillator in whichmultiple quartz oscillators of the type shown in FIG. 1 are arranged onthe same substrate.

FIG. 8 is a plan view from above of a batch-type liquid-phase quartzoscillator sensor in which a chip quartz oscillator in accordance withthe present invention is arranged in each tub-like vessel for containinga sample solution.

FIG. 9 is a sectional view along the line E-F in FIG. 8.

FIG. 10 is a circuit diagram showing the electrical configuration of aquartz oscillation device of the present invention.

FIG. 11 is a block diagram of a flow-type liquid-phase quartz oscillatorsensor device in which a chip quartz oscillator in accordance with thepresent invention is installed.

FIG. 12 is a graph showing an experimental result of the stability inoutput signal depending on flow rate in the flow-type liquid-phasequartz oscillator sensor comparing the chip quartz oscillator of thepresent invention against the previous-type chip quartz oscillatorsupported with O-ring.

FIG. 13 is a graph showing an experimental result of the stability inoscillation frequency output, comparing a quartz oscillation device inaccordance with the present invention and an ordinary quartz oscillationdevice operated from an AC power source.

FIG. 14 is a schematic illustration showing the prior art method forsupporting a circular quartz oscillator with O-rings.

FIG. 15 is a sectional view along the line G-H indicated in FIG. 14.

FIG. 16 is a sectional view of the flow-type liquid-phase quartzoscillator sensor in which the chip quartz oscillator indicated in FIG.14 is installed.

FIG. 17 is a graph showing an experimental result in which is shown achange in oscillation frequency due to molecules binding to a chipquartz oscillator in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Several embodiments of the present invention will be described below indetail with reference to the drawings. However, it is to be understoodthat the present invention is not intended to be limited to the specificembodiments but covers all variations and modifications covered by theappended claims. It should be assumed that same reference numeral orsymbol designates the same or a similar component in the drawings.

FIG. 1 is a plan view from above schematically showing the firstembodiment of the chip quartz oscillator of the present invention, andFIG. 2 is a sectional view along the line A-B indicated in FIG. 1. Inthese figures, the chip quartz oscillator S has a rectangular quartzoscillator 2 placed on the upper surface 1′ of a substrate 1. Substrate1 is made of any material which is rigid, non-conducting or able toretain a non-conducting coating, non-soluble in the liquids being testedand preferably inexpensive and easy to work with. Many engineeringplastics, metals and ceramics are suitable for this use, in particularthe types used for making circuit boards. The quartz oscillator 2 has adetection electrode 3 on a first surface 2′ and a non-detectionelectrode 3″ on the opposite second surface 2″ i.e. in this case theside facing towards the upper surface 1′ of the substrate 1. In anexample of an embodiment of the present invention the quartz oscillator2 is in the order of 4 mm long, 1.6 mm wide and 60 μm thick, otherdimensions and shapes are of course possible. Thus the first and secondsurfaces have an area of 6.4 mm² and the side-wall 2′″ of the oscillatoris 60 μm deep.

In order to make an electrical connection to the corresponding portionof the substrate 1, a lead electrode 3′ (also called a partialelectrode) made of a thin metal layer, is connected to the detectionelectrode 3. The lead electrode 3′ extends across the surface of thequartz oscillator to its edge, over the edge and down the side of thequartz oscillator 2 and around the bottom edge of the side-wall to theunderside of the quartz oscillator where it is connected, preferably byusing a small amount of an electrically conducting bonding agent (notshown), to a first terminal 4 preferably made of a thin metal layer onthe substrate 2. Similarly, the non-detection electrode 3″ on theopposite surface of the quartz oscillator 2 is electrically connected bya lead electrode 3′″ to a second terminal 4′ on the upper surface ofsubstrate 1, again preferably by using an electrically conductingbonding agent (not shown). Each of the terminals 4 and 4′ iselectrically connected to an external terminal placed on the back of thesubstrate 2 (i.e., on the surface opposite to the one with the quartzoscillator 2) by using an electrical connection such as a via throughthe substrate 2. With this configuration, a voltage can be applied tothe detection electrode 3 and the non-detection electrode 3″ from theopposite surface of the substrate 1 to that where the quartz oscillator2 is placed.

In order to prevent a short circuit between the detection electrode 3and the non-detection electrode 3″ caused by an electrically conductingfluid coming in contact with the non-detection electrode placed on theback of the quartz oscillator 2, the side-wall 2′″ of the quartzoscillator 2 is flexibly fixed and sealed along the whole of itscircumference to the substrate 1 by using an elastic bonding agent 5.This bonding agent is preferably not soluble in the liquids being testedand can be, for example, a silicon-resin bonding agent. It shouldpreferably be mobile enough, when it is being applied to the chip, tospread easily while being viscous enough to not penetrate into thecontact area between the oscillator and support. After being cured, itshould also be elastic enough to allow the oscillator's stabilisedmotion but it should no longer be mobile. As shown in FIG. 3, which isan enlarged view of the circled part of FIG. 2, the elastic bondingagent 5 is used to fix the side-wall 2′″ of the quartz oscillator 2 tothe substrate 1; the minimal possible amount of the bonding agent isused in order to keep both top surface (the surface with the detectionelectrode 3) and bottom surface (the surface with the non-detectionelectrode 3″) of the quartz oscillator 2 free from the bonding agent asthis would otherwise adversely affect the performance of the quartzoscillator.

In the chip quartz oscillator S with this configuration, because of theflexible attachment of the quartz oscillator 2 to the substrate 1 by anelastic bonding agent, it is possible to minimise resistance forces dueto the attachment to the substrate 1 and to keep the decrease in Q to aminimum for a bulk-wave-mode thickness shear vibration in an AT-cutquartz oscillator or the like. Further, once the quartz oscillator 2 isfixed to the substrate 1, i.e. once the bonding agent has cured, theattachment does not undergo any changes when the chip is mounted in adevice as the substrate absorbs all the mounting forces, and thereforeno mounting forces are applied to the oscillator chip. This gives theadvantage that the state of oscillation is highly reproducible when usedrepeatedly, a significant advantage when compared to a prior art quartzoscillator fixed by the previous method of mechanical tightening withO-rings or gaskets.

As described earlier, in a previous liquid-phase sensor, a gaseouscavity has been often placed on the back of a quartz oscillator and thequartz plate has been supported at end points thereof, and therefore,there has been the disadvantage that the plate is distorted due tovariations in the fluid pressure of a sample solution. This causes the Qto decrease markedly depending upon the pressure and, as a result, theoscillation becomes unsteady or halts. However, in the presentinvention, the steady oscillation can be maintained as the distortion ofthe quartz oscillator 2 is prevented, because the oscillation surface,facing the substrate 1, of the quartz oscillator 2 is supportednon-adhesively but distributively in contact with the surface of thesubstrate 1. This is a great advantage over the prior art quartzoscillator, which is sensitive to flow rate changes, is substantiallyunusable under conditions of medium or high flow rate that causes largepressure fluctuations because of pulses in the flow of liquid, and alsotends to limit the use of reciprocating pumps which produce highlypulsating flows. However, these problems can be substantially avoidedwith the chip quartz oscillator S of the present invention.

The above-mentioned term “non-adhesively” means that the surface of thequartz oscillator facing the substrate 1 is not bonded to the substrate1 nor is it intentionally kept lifted apart from the substrate;therefore, the back surface can freely oscillate transversely.“Distributively” means that the mounting forces are distributed over thecontact area between the substrate 1 and quartz oscillator, preferablydistributed evenly over the contact area.

Additionally, in a chip quartz oscillator S of the present invention, itis possible to keep the detection electrode 3 and the non-detectionelectrode isolated electrically from each other even in a conductingsample solution, because the quartz oscillator 2 is sealingly bondedalong its circumference to the substrate 1 by the waterproof elasticbonding agent 5. Furthermore, in the prior art it was necessary toattach a wire directly to the surface electrode of the quartz oscillatorduring installation. However, in the present invention, the chip quartzoscillator S is an easily replaceable unit because an externalelectrical connection for the upper electrode can be arranged on thebottom surface of the substrate 1 along with the connection for thelower electrode, thereby advantageously achieving simple installation.In the present invention, there is another advantage that the fragilequartz oscillator can be protected against mechanical damages since thechip quartz oscillator can be handled or replaced on a chip-unit (i.e.chip and substrate) basis, i.e. contact with the fragile chip can beavoided.

A method for manufacturing a chip quartz oscillator in accordance withthe present invention can comprise the following steps:

-   detection and non-detection electrodes and lead electrodes are    vapour deposited onto a quartz oscillator;-   a substrate having a suitable shape and size is provided with    electrodes on the surface which is intended to face the quartz    oscillator and through holes from these electrodes leading to the    opposite side of the substrate;-   conductors leading from the electrodes on the surface of the    substrate are provided in the through holes;-   conducting bonding compound is applied to the electrodes on the    substrate and the quartz oscillator is placed on the substrate with    its lead electrodes in contact with the conducting bonding compound;-   the conducting bonding compound is cured;-   a flexible when cured bonding compound is applied, for example    manually by means of a thin pin while viewing with a microscope, or    automatically by a robot, around the circumference of the quartz    oscillator to bond the side wall of the quartz oscillator to the    surface of the substrate; and-   any excess bonding compound on the upper surface of the quartz    oscillator is removed.

The above is an example of a rectangular quartz oscillator 2, but a chipquartz oscillator S, in accordance with the present invention, can alsobe achieved by using quartz oscillators having other shapes. FIG. 4 is aplan view from above schematically showing a second embodiment of a chipquartz oscillator of the present invention, and FIG. 5 is a sectionalview along the line C-D indicated in FIG. 4. In a chip quartz oscillatorS of this second embodiment, a circular quartz oscillator 6 is arrangedon the substrate 1. The quartz oscillator 6, for example, has a circulardetection electrode 7 on the first surface 6′ opposite to the substrate1. A lead electrode 7′ made of a thin layer of vapour-deposited metal iswired from an appropriate portion of the detection electrode 7, extendsin the direction of the radius of the quartz oscillator 6 on the surface6′ thereof, goes down the side-wall 6′″ of the quartz oscillator 6, andextends around to the back surface 6″ which faces the substrate 1. Theback portion of the lead electrode 7′ of the quartz oscillator 6 iselectrically connected to the terminal 4 on the substrate 1, preferablyusing a minimum area and thickness compatible with a reliableconnection, by using an electrically conducting bonding agent (notshown). Likewise, a non-detection electrode 7″ on the other surface ofthe quartz oscillator 6 is electrically connected to the terminal 4′ onthe substrate 1, which faces the terminal 4 thereon in the direction ofthe diameter thereof, in a minimum area and thickness by using anelectrically conducting bonding agent (not shown). This is in order tominimise the forces acting on the chip. In the same manner as in thefirst embodiment, each of the terminals 4 and 4′ is electricallyconnected to an external terminal placed on the back of the substrate 2(namely, the surface opposite to the one with the quartz oscillator 2)by using an electrical connection such as a via through the substrate 2.With this configuration, a voltage can be applied from the dry, rearsurface of the substrate 1, where the quartz oscillator 6 is not placed,to the detection electrode 3 and the non-detection electrode.

In the second embodiment, the quartz oscillator 6 is also fixed flexiblyon the substrate, by bonding the side of the quartz oscillator 6 withthe surface of the substrate 1 by using the elastic bonding agent 5.According to this, as in the first embodiment, it is possible to achievethe desired surface-contacting, non-adhesive, distributed support of theoscillation surface of the quartz oscillator 6 onto the surface of thesubstrate 1.

Several application examples will be described here in regard to thechip quartz oscillator S of the present invention. FIG. 6 is a sectionalview showing an example of a flow-type liquid-phase quartz oscillatorsensor using a chip quartz oscillator S of the first or secondembodiment described by referring to FIGS. 1-5. An inflow entrance 9 anda drain hole 10 are arranged in the vessel 8, to enable a samplesolution to enter the vessel and come into contact with the detectionelectrode of the chip quartz oscillator S inside-the flow-typeliquid-phase quartz oscillator sensor T. The substrate of the chipquartz oscillator S is fixed between cushioning material 11, such as anelastic body such as an O-ring or a flexible gasket, and a preferablyelastic electric junction 12, such as an elastic metal such as flatspring or dampening pin. The cushioning material 11 is used topreventing the sample solution from flowing into the region around therear side of the substrate of the chip quartz oscillator S, and theelectric junction 12 is used for electrically connecting the terminalsof the electrodes placed on the back of the substrate 1 of the chipquartz oscillator S to the circuit board 13 which is convenientlyarranged inside the liquid-phase sensor. The circuit board 13 cancomprise the circuit layout of the oscillation circuit, together with aquartz oscillator, and appropriate circuit components arranged on theboard.

The temperature of the chip quartz oscillator S is preferably keptconstant to reduce a source of errors by using an appropriate heating orcooling element such as a Peltier element (not shown).

The mounting forces are directly applied to the quartz oscillatorthrough the elastic body in the prior art. However, as shown in FIG. 6,in the present invention, the chip quartz oscillator S is fixed flexiblyin the vessel 8 by using the elastic bodies that are the cushioningmaterial 11 and the electric junction 12. Additionally, the substrate 1is fixed in the vessel 8, thereby preventing the mounting forces frombeing applied to the quartz oscillator 2 or 6. In addition to this, evenwhen micro-deformation of the vessel 8 occurs due to minute changes oftemperature or flow rate during the operation, such micro-deformationsare absorbed by the cushioning material 11 and elastic electric junction12. Broadening the range of condition where the flow-type liquid-phasequartz oscillator sensor T is usable with high reproducibility, thesestructural features contribute to the achievement of a liquid sensorwith higher reliability.

The cushioning material 11 such as O-ring or gasket is used forconvenience of replacing the chip quartz oscillator S, and therefore, itcan be substituted with any other functional equivalents, for example, acombination of cushioning material and inner surface of the vessel 8 inone. Similarly, the elastic electric junction 12 is not essential: forexample, the electric junction may be omitted, and a flexible contact onthe circuit board 13 may be connected directly to a terminal on the backof the substrate 1 of the chip quartz oscillator S. Further, it ispreferable to connect a flow tube to either one, or both, of the inflowentrance 9 and the drain hole 10 in the flow-type liquid-phase quartzoscillator sensor T, according to need.

FIG. 7 is a plan view from above showing the chip quartz oscillator S inwhich multiple units of the quartz oscillator 2 of the type shown inFIG. 1 are arranged on a single unit of the substrate 14. This shows agrid-like arrangement on a single substrate 14 of multiple units of thefirst and second embodiments of the present invention. It is possible toapply power to each of the quartz oscillator 2 or 6 from the singlesurface, which is opposite to the one with the quartz oscillator 2 or 6,of the substrate 14 in this case as well. Each unit of the quartzoscillator 2 or 6 can independently be bonded to the substrate 14 andconnected electrically in the same manner as described previously forthe first and second embodiments of the present invention.

In the structure indicated in FIG. 7, not only multiple units of thequartz oscillator 2 or 6 but also multiple units of the electrode 3 arearranged in a matrix, thereby permitting simultaneous detection ofdifferent types of targets in a solution in contact with the matrix byarranging a different molecular ligand on each detection electrode. Inaddition, the chip quartz oscillator can be moved around or replaced byhandling a single unit of the substrate 14 alone, and thus it ispossible to improve the efficiency of operation for detection. Multipleflow-type liquid-phase quartz oscillator sensors can be used for eachpurpose, and there is no restriction in respect of the number and thearrangements thereof.

FIG. 8 is a plan view from above showing an example of a batch-typeliquid-phase quartz oscillator sensor U having multiple units of thechip quartz oscillator S of the present invention arranged thereon, andFIG. 9 is a sectional view along the line E-F indicated in FIG. 8. Inthese figures, a frame 15, which is made of electrical insulatingmaterial has an opening on upper side, is partitioned longitudinally andtransversely by separators 16, for example in the form of waterproofinterconnected walls, to form multiple units of the tub-like vessel 17arrayed in a lattice therein, and a chip quartz oscillator S inaccordance with the first or second embodiment of the present inventionis fixed in each tub-like vessel 17. Each tub-like vessel 17 can hold asample of the sample solution therein, and the detection electrode 3 or7 of the chip quartz oscillator S placed therein is exposed to thesample solution.

As can be seen from the configuration indicated in FIGS. 8 and 9, in thebatch-type liquid-phase quartz oscillator sensor U, a single unit of thechip quartz oscillator S can be placed in every tub-like vessel 17,thereby achieving simultaneous measurement of multiple solutions to betested as well as improving the efficiency of operation for detection.In addition, each tub-like vessel 17 is isolated from others, and, as aconsequence, it is possible to perform detection with only a single unitof the tub-like vessel; thus the batch-type sensor U is useful forsamples (for example, samples with high viscosity or containing testsubstances that are detectable after a period of relatively longreaction time in the detection vessels), which can hardly be detectedwith the flow-type vessel as shown in FIG. 6.

Multiple batch-type liquid-phase quartz oscillator sensors U can be usedfor many purposes, and there is no restriction in respect of the numberand the arrangement thereof. The shape of the tub-like vessel 17 is notlimited to the rectangular shape shown in the figure, and any shapes areacceptable for the vessel in as far as the vessel is capable of keepingthe chip quartz oscillator S inside. In addition, any arrangement of thechip quartz oscillator S in the tub-like vessel 17 is acceptable, as faras the detection electrode 3 or 7 thereof is exposed to sample solutionand an electrical connection is ensured between the terminal on the backof the substrate 1 and the corresponding circuit in each chip quartzoscillator 12; for example, the chip quartz oscillator S can beinstalled on a side of the frame 15. Further, it is possible to arrangethe chip quartz oscillator S upside down at the boundary between samplesolution and the vapour phase thereof so that the detection electrode ofthe chip quartz oscillator S is placed above, and in contact with, thesample solution. It is also possible to mount the quartz oscillator 2 or6 on the surface of the bottom part of the frame 15, by omitting thesubstrate 1 of each chip quartz oscillator S and assuming that thesurface on the bottom or side of the frame 15 is equivalent to thesubstrate 1.

FIG. 10 is a circuit diagram schematically showing an example of theconfiguration of a quartz oscillator device in accordance with thepresent invention, which contains the above-describe chip quartzoscillator S as a component. As shown in this figure, the quartzoscillator device V has an oscillation circuit section OSC, aphotocoupler section PC, a driving section DR and a power source sectionPS.

The oscillation circuit section OSC consists of an inverter 18, aresistor 19, a chip quartz oscillator 20, a resistor 21, and acapacitors 22 and 23; the inverter 18 constitutes a NOT circuit. Theresistor 19, which is connected between the output and input terminalsof the inverter 18, is a feedback element. The resistor 21 is an elementfor limiting the current flowing into the chip quartz oscillator 20, andtogether with the resistor 21, the chip quartz oscillator 20 isconnected between the output and input terminals of the inverter 18. Thedetection electrode of the chip quartz oscillator 20, which operates asa sensor, is in contact with a sample solution. The capacitor 22 isconnected between the detection electrode of the chip quartz oscillator20 and the ground; the capacitor 23 is connected between thenon-detection electrode of the chip quartz oscillator 20 and the ground.

The output of the oscillation circuit section OSC is transmitted to thephotocoupler section PC through the driving section DR. The drivingsection DR consists of an inverter 24, series resistors 25, 26, and 27,and a capacitor 28 that is connected in parallel with the resistor 26;an end of the resistor 27 is connected with a light-emitting element inthe photocoupler section PC. The anode of the light-emitting element inthe photocoupler section PC is connected through the resistor 29 withthe power source voltage VCC. The output of the quartz oscillator deviceV is outputted from the photoreceptor element in the photocouplersection PC.

In order to reduce mains noise, the power source section PS, whichsupplies the power source voltage to each component of the quartzoscillator device V, preferably consists of a battery 30, a capacitor 31that is connected in parallel to the battery 30, a constant-voltagecircuit 32, and a capacitor 33 required for connecting the outputterminal of the constant-voltage circuit 32 to ground.

Each section constituting the quartz oscillator device V and the meansfor keeping the chip quartz oscillator in contact with sample solutionare preferably installed in the metal vessel 34, thereby electricallyshielding each component in the metal vessel 34. The metal vessel 34 ispreferably made removable, and, for example, battery replacement can beperformed after removing the metal vessel 34. The operability can beimproved by substituting the element placed between the terminal M and Nof the battery with the element placed between the terminals m and n ofthe switching circuit SW consisting of the battery 30, a relay 36, anexternal switch 35 and a driving direct-current power source voltage VDDthereby switching the oscillation circuit section OSC on and off, byinstalling the external switch 35 outside the metal vessel 34, and byconnecting the external switch 35 through the relay 36 with theoscillation circuit section OSC to keep the electrical shield effective.

Thus, the output of the oscillation circuit section OSC is electricallyisolated from external devices such as a frequency counter by using thephotocoupler section PC, the power source voltage is supplied to eachcircuit section from the battery 30, and the whole is shielded byinstalling it in the metal vessel, thereby preventing the fluctuation ofoscillation frequency caused by the variation of the power sourcevoltage due to external noises and, as a consequence, achieving a steadyoscillation frequency thereof. Furthermore, the configuration shown inFIG. 10 is particularly advantageous and has a prominent effect, whenthe quartz oscillation device must be isolated electrically from otherdevices, for example, when multiple quartz oscillators are arranged in amatrix on a substrate as shown in FIG. 7, when multiple electrodes areexposed to a sample solution, or when it is arranged in a place where itcan establish an inductive connection with other electrical devices (forexample, a temperature controller) through the sample solution or canestablish direct electrical continuity to the devices.

A quartz oscillator is usually operated by a direct-current power sourceof 5 V. It has been recognised that it tends to change its oscillationfrequency in response to even small variations in the applied powervoltage when its Q decreases markedly such as in the case of immersingit into a liquid phase. For example, the change of 1 mV in appliedvoltage caused a change of oscillation frequency of about 10 Hz in thecase of a 27-MHz AT-cut quartz oscillator. In order to achieve anoscillation frequency output stability in the order of Hz or sub-Hertz,the power source voltage must have a stability in the order ofmicro-volts. This means that it is not negligible that there areinductive external noises coming into the quartz oscillation devicethrough the wiring and micro-fluctuations of voltage caused by noisesoriginating from external devices such as a power source circuit.However, it is not easy to cancel such micro-fluctuations by using acompensator. By taking these technical backgrounds into consideration,in the quartz oscillation circuit of the present invention, perfectelectrical isolation is achieved by installing the battery and otherrequired circuit elements in a shield as well as by designing theconfiguration where the oscillation output is drawn out through aphotocoupler. Thus, with the present invention it is possible toconsiderably reduce the possibilities of external noises coming in, andto achieve a high stability of oscillation frequency output.

FIG. 11 is a schematic diagram showing an example of a configuration forthe practical use of a flow-type liquid-phase quartz oscillator sensor Twhere a chip quartz oscillator S according to the present invention isintegrated, which includes peripheral devices. The flow-typeliquid-phase quartz oscillator sensor device 39 consists of theflow-type liquid-phase quartz oscillator sensor T, which is describedabove by referring to FIG. 6, a heating or cooling element such as aPeltier element for keeping the temperature of the sensor constant, anda thermally insulated outer vessel. The electrical shield as describedabove with reference to FIG. 10 is achieved by using a metal vesselcapable of electrical insulation as the outer vessel for the flow-typeliquid-phase quartz oscillator sensor device 39 or by enclosing theflow-type liquid-phase quartz oscillator sensor T with another metalvessel as shown in FIG. 11. The sample solution, after being placed inthe vessel for supplying sample solution 42, is allowed to flow throughthe flow tube 45 by using the pump 41, which is capable of providing aconstant flow rate without a pulsating flow, and the solution goesthrough the valve with injector 43 and is supplied from the inflowentrance 9 to the flow-type liquid-phase quartz oscillator sensor T; thesolution is discharged through the drain hole 10 to the waste liquidcontainer 47. There is a possibility that the detection electrode 3 ofthe chip quartz oscillator S becomes conductive to the outside throughthe sample solution when the flow tube 45 is removed from the flow-typeliquid-phase quartz oscillator sensor device 39 and, as a result, theelectrical shielding by the metal vessel fails to work. However,usually, the effective resistance of sample solution is relativelylarge, and the conducting effect is negligible in practice and theshielding effect is ensured when a non-conducting plastic tube withsmall inner and outer diameters (e.g. an outer diameter of about 1 mmand inner diameter of 0.25 mm or less) is used as the flow tube 45.

A solution containing substances to be tested can be injected to thetube for test solution 40 through the valve with injector 43 by using aninjection syringe, and then the solution can be supplied to theflow-type liquid-phase quartz oscillator sensor T by turning the switchof the valve with injector 43. The output oscillation frequency of theflow-type liquid-phase quartz oscillator sensor T can be transmittedthrough a coaxial cable 46 to a frequency counter 38, measured by thecounter 38 at fixed intervals or continuously, and then transmitted byan interface such as GPIB or RS232C through a communication cable 44 toa computer 37. The computer 37 with the interface such as GPIB or RS232Cpreferably is made capable of controlling the pump 41 and the valve withinjector 43 through a communication cable 44. The procedure ofperforming the measurement comprises the steps of: applying power to theflow-type liquid-phase quartz oscillator sensor device 39 to initiatethe oscillation; actuating the thermo-controller of the liquid-phasequartz oscillator sensor 39; simultaneously allowing a liquid to flow ata constant rate with the pump 41; and turning the valve with injector 43and allowing a sample solution to flow into the flow-type liquid-phasequartz oscillator sensor T when the output oscillation frequency becomessteady in the flow-type liquid-phase quartz oscillator sensor T. Theoutput oscillation frequency changes in proportion to the minute changein mass caused by sample adsorption on and release from the detectionelectrode 3 of the chip quartz oscillator S. The change can be measuredin the frequency counter and the data can be captured and recorded inthe computer 37 at fixed intervals and/or continually. The examplesdescribed below were measured by using this system configuration, theflow-type liquid-phase quartz oscillator sensor device and theperipheral device W.

FIG. 12 shows an experimental result of the stability of output signalagainst the flow rate of a sample solution; a prior art-type quartzoscillator directly supported with O-rings as indicated in FIGS. 14 and15 was installed in the flow-type liquid-phase quartz oscillator sensorindicated in FIG. 16, and a chip quartz oscillator S in accordance withthe present invention indicated in FIGS. 1 and 2 was installed in theflow-type liquid-phase quartz oscillator sensor T; the results obtainedby the two types of sensors are compared with each other in this figure.In each case, the quartz oscillator is placed at the position of thequartz oscillator 20 indicated in FIG. 10. The ordinate indicates therelative oscillation frequency of the quartz oscillation device asdesigned above; the abscissa indicates time. Pure water was used as asample solution, i.e. no solution containing a substance to be testedwas injected, and therefore, no adsorption-and-release phenomenonoccurred on the electrode during the measurement. Accordingly, duringthe experiment, changes in oscillation frequency are understood not tobe derived from mass change.

In FIG. 12, curves, a, b, c, and d represent output frequency responsein the flow-type liquid-phase quartz oscillator sensor using theprevious-type direct-support with O-ring, and curves, α, β, γ, and δrepresent output frequency response in the flow-type liquid-phase quartzoscillator sensor T with a chip quartz oscillator S in accordance withthe present invention. The flow rate of sample solution was 0 μl/minutein curves a and α; 10 μl/minute in curves b and β; 50 μl/minute incurves c and γ; 100 μl/minute in curves d and δ.

The curves, a-d in FIG. 12 indicates that fluctuation of the frequencyincreases with increases in the flow rate in the case of theprevious-type quartz oscillator directly supported with O-ring. This isbecause the quartz oscillator directly supported by O-rings is easilydistorted by the fluid pressure of the sample solution. However, asindicated by the curves, a-δ, the inventive chip quartz oscillator S ishardly affected by increases in fluid pressure and as a resultfluctuations of the oscillation frequency are very small.

FIG. 13 is a graph showing an experimental result, where stability inoutput oscillation frequency obtained by the quartz oscillator device Vshown in FIG. 10 is compared with that obtained by an ordinary quartzoscillation device operated with AC power source. The ordinate indicatesfrequency (Hz); the abscissa indicates time (second). The measurementwas performed by using the flow-type liquid-phase quartz oscillatorsensor T with the inventive chip quartz oscillator S indicated in FIG.6. Like in the example described above, pure water was used as a samplesolution and no solution containing a substance to be tested wasinjected. In the ordinary quartz oscillation device operated with ACpower source, power is supplied to the quartz oscillator by rectifyingand dropping down the voltage from the commercial AC line (at e.g. 100volts), and the oscillation output is directly connected to thefrequency counter. Thus, as seen from curve e, output frequency of theordinary quartz oscillation device operated with AC power source variesconsiderably depending on external noises coming through the wiring aswell as noises from the power source circuit. However, as seen fromcurve ε, in the quartz oscillation device V indicated in FIG. 10, outputof the oscillation device is connected through a photocoupler to anexternal device, the power is supplied from a battery, and the wholeoscillation device is enclosed and shielded with a metal vessel, therebyelectrically insulating the device from external devices; thusfluctuations of oscillation frequency, which are due to noises in thepower source circuit, are extremely small and steady oscillation can beachieved.

As understood from the above description of the several embodiments andapplication examples, in the present invention, the side-wall of aquartz oscillator is designed to be flexibly attached to the surface ofthe substrate, while the surface of the oscillator facing the surface ofthe substrate is not attached to the surface of the substrate, therebyachieving surface-contacting, non-adhesive, distributed support of thequartz oscillator by the substrate. This design has the extraordinaryeffect that the quartz oscillator is hardly distorted even when havingdeformation stresses caused by change in property of sample solution incontact with the quartz oscillator or caused by device operation such asflow of sample solution, and as a result steady oscillation is achieved.In addition, it has the merit to protect the quartz oscillator againstmechanical damages since the quartz oscillator can be moved around orreplaced without handling it directly as it can be handled by grippingthe substrate.

It has also the great advantage to ensure the steady operation of theoscillation device; even when multiple quartz oscillators operatesimultaneously while being immersed in a conducting fluid, electricalinterference such as short circuits is not generated between the quartzoscillation devices each of which contain a quartz oscillator, becauseeach quartz oscillator is fixed on one side of the substrate and acircuit component electrically connected to the quartz oscillator isplaced on the other side of the substrate.

Furthermore, according to the present invention, all the electricalcomponents required for the quartz oscillation device can be insulatedelectrically and isolated from other electrical components, because thequartz oscillation circuit with the chip quartz oscillator, togetherwith the power source section required for the circuit is designed to beinstalled and shielded electrically in a metal vessel. Additionally, theoutput from the oscillation circuit is designed to be connected througha photocoupler to an external device. Accordingly, this removesfluctuations of oscillation frequency caused by changes in the powersource voltage due to external noises, thereby ensuring the steadyoscillation of the liquid-phase sensor and further improving theeffective sensitivity of the liquid-phase sensor.

FIG. 17 shows a graph displaying experimental results obtained from chipquartz oscillators in accordance with the present invention used for thespecific detection of a protein-protein interaction. The x-axis of thegraph displays time in seconds and the y-axis shows the change inoscillation frequency of the oscillators. Two chip quartz oscillators,each with a nominal oscillation frequency of 27 MHz, were used in thisexperiment. The first oscillator was prepared with a mouseanti-myoglobin (Biacore) pre-immobilized sensor surface constructedthrough a self-assembled monolayer of 3,3′-dithiodipropionic aciddeposited on its gold detection electrode while the second oscillatorwas prepared with a bovine serum albumin (BSA, Amersham PharmaciaBiotech)-pre-immobilized sensor surface constructed through aself-assembled monolayer of 3,3′-dithiodipropionic acid deposited on itsgold detection electrode.

A sample of 50 μl of 5.0 μg/ml (0.30 μM) sheep myoglobin (MW. 16,923,Biacore) solution was injected onto each oscillator using 50 mM HEPESbuffer (pH 7.4) with 0.2 M NaCl as a running buffer. The flow rate was100 μl/min and the operating temperature was 25.00° C.

Upon the injection of myoglobin solution at time A, the chip quartzoscillator having a myoglobin-pre-immobilised surface responded to yielda relatively large decrement of the frequency (curve C), showing thatmyoglobin had become bound to its detection electrode and demonstratingthat a specific protein-protein interaction can be measured by anappropriately prepared sensor. The oscillator with the nonspecificsurface (BSA-pre-immobilised surface) only showed a low response to theanalyte (curve B) and this was mainly due to a minute change in thedensity of the buffer upon the injection of the solute. This illustratesthat a chip quartz oscillator in accordance with the present inventionmay be used to detect the presence of specific molecules present in aliquid which is in contact with the detection electrode of the chipquartz oscillator.

The above mentioned embodiments are intended to illustrate the presentinvention and are not intended to limit the scope of protection claimedby the following claims.

EXPLANATION OF REFERENCE NUMERALS

1: substrate, 1′: upper surface of substrate, 2: rectangular quartzoscillator, 2′: first surface, 2″: second surface, 2′″: side-wall 3:detection electrode, 3′: lead electrode, 3″ non-detection electrode,3′″: lead electrode 4: terminal, 4′: terminal, 5: elastic bonding agent,6: circulat quartz oscillator, 6′: first surface, 6″: second surface,6′″: side-wall, 7: detection electrode, 7′: lead electrode, 8: vessel,9: inflow entrance, 10: drain hole, 11: cushioning material, 12:electric junction, 13: circuit board, 14: substrate, 15: frame, 16:separator, 17: tub-like vessel, 18: inverter, 19: resistor, 20: chipquartz oscillator, 21: resistor, 22: capacitor, 23: capacitor, 24:inverter, 25: resistor, 26: resistor, 27: resistor, 28: capacitor, 29:resistor, 30: battery, 31: capacitor, 32: constant-voltage circuit, 33:capacitor, 34: metal vessel, 35: external switch, 36: relay, 37:computer, 38: frequency counter, 39: flow-type liquid-phase quartzoscillator sensor device, 40: tube for test solution, 41: pump, 42:vessel for supplying sample solution, 43: valve with injector, 44:communication cable, 45: flow tube, 46: coaxial cable, 47: waste liquidcontainer, 48: quartz oscillator, 49: O-ring or gasket, 50: vessel, 51:inflow entrance, 52: drain hole, 53: circuit board, S: chip quartzoscillator, T: flow-type liquid-phase quartz oscillator sensor, W:flow-type liquid-phase quartz oscillator sensor device and peripheraldevices, U: batch-type liquid-phase quartz oscillator sensor, V: quartzoscillation device, OSC: oscillation circuit section, PC: photocouplersection, DR: driving section, PS: power source section, SW: switchingcircuit.

1. A chip quartz oscillator comprising a plurality of quartz ofoscillators (2; 6), each having a first surface (2′; 6′) and a secondsurface (2″; 6″) joined by a side-wall (2′″; 6′″), wherein each quartzoscillator further has a detection electrode (3; 7) on said firstsurface (2′; 6′) and a non-detection electrode (3″, 7″) on said secondsurface (2″; 6″) and wherein each quartz oscillator (2; 6) is flexiblymounted on a substrate (14), and further wherein the surface (2″; 6″) ofsaid quartz oscillator (S) facing towards said substrate (1; 14) is incontact with said substrate (1; 14) but does not adhere to saidsubstrate (1; 14).
 2. A chip quartz oscillator comprising a plurality ofquartz of oscillators (2; 6), each having a first surface (2′; 6′) and asecond surface (2″; 6″) joined by a side-wall (2′″; 6′″), wherein eachquartz oscillator further has a detection electrode (3; 7) on said firstsurface (2′; 6′) and a non-detection electrode (3″, 7″) on said secondsurface (2″; 6″) and wherein each quartz oscillator (2; 6) is flexiblymounted on a substrate (14), and further comprising at least a quartzoscillation circuit section (OSC) for causing said quartz oscillator tooscillate and to output a signal relating to the oscillation frequencyof said quartz oscillator; a photocoupler section (PC) for transmittingthe output from the quartz oscillation circuit section to an externaldevice, a power source section (PS) containing a battery for supplyingvoltage to the quartz oscillation circuit section (OSC) and thephotocoupler section (PC), and a shield for insulating the quartzoscillation circuit section, the photocoupler section, and the powersource section in order to prevent fluctuation of oscillation frequencycaused by external noises.